Normal sudoku rules apply. A digit in column 1 indicates the column in which the digit 1 appears in that row. (Eg If r4c1 is a 6, r4c6 is a 1). A digit in column 5 indicates the column in which the digit 5 appears in that row. A digits in column 9 indicates the column in which the digit 9 appears in that row. Digits in cells with a shaded square must be even. Cells separated by a single knight's move (in chess) cannot contain the same digit.